Materials Science Forum Vols. 626-627

Abstract: Grind-hardening is a type of composite technology, which utilizes the dissipated heat in the grinding zone for hardening of the workpiece surface layer. The temperature of the workpiece surface, when heated by the grinding, is higher than the austenitizing temperature for short time, then it is lowered by quick cooling causing martensitic transformation to happen in the surface layer of the workpiece. The residual stress is formed by the thermal stress, phase transformation stress and mechanical stress in the grind-hardening layer. In this paper, the forming mechanism of the residual stress in grind-hardening technology is analyzed in theory; the residual stress field in the surface layer is calculated by the finite element, according to changes in the specific volume of the microstructure, the temperature field and the temperature history of the surface layer at different depths. The temperature field is achieved by computer simulation technology. The result of residual stress calculations indicates that the change tendency of the grind-hardening residual stress in the finite element analysis is consistent with the experiments.

Abstract: A preliminary study of Numerical Controlled Electrochemical Turning (NC-ECT) technology was presented in this paper. NC-ECT is suitable for machining revolving workpieces which are made of difficult-to-cut materials or have low rigidity, and it is difficult or expensive for machining these workpieces by use of traditional turning or traditional Electrochemical Machining (ECM) method. To carry out the study, an experimental setup was developed on the basis of a common lathe, and a kind of inner-spraying cathode with rectangle section outlet was designed according to the process of machining cylindrical surface. First, the NC-ECT method was simply described. Then, considering the structure of the cathode and the process of machining, the method for calculating the inter-electrode gap in machining the cylindrical surface was given. Finally, the experiments of machining the cylindrical surface were carried out. Experiments showed that the calculated inter-electrode gaps are well consistent with the actual value of the machining process, which decreases with the increase of the rotational speed of workpiece and increases almost linearly with the increase of the working voltage. Experiments also showed that the inter-electrode gap keeps a certain relationship with the working current, the inter-electrode gap can be controlled according to working current in the machining process.

Abstract: The technology of electro-spark deposition has been investigated and the thickness of H13 steel coating up to 16.2μm has been achieved by applied SH-1000 electro-spark deposition power. It analyzed the effect of parameters such as voltage, discharge frequency, argon gas flow and rate deposition on the deposition thickness. The optimum deposition parameters have been selected through the orthogonal design. In order to improve coating quality, a novel method based on ultrasonic-assisted electro-spark deposition has been put forward.

Abstract: The three dimensional (3D) coupling model is set up for analyzing the energy reflection and absorption on the kerf using ray tracing method after the laser beam cutting nonmetallic materials with high absorptance through multiple reflections. The laser beam characterized by focused gauss beam and fresnel absorption on the kerf are taken into account. The influences of the polarization on the absorbed intensity both in the front and the two walls are also discussed. Results indicate the differences of absorptive intensity among the three polarized lights are relatively small compared to metal. Thus, the polarization has little effects on the kerf of nonmetallic materials with high absorptance. The experimental results also agree well with the theoretical analysis.

Abstract: A nanosecond pulse power supply for micro-ECM (Electrochemical Machining) has been developed, and the minimum pulse on-time is 50 ns. After the influence of ultra-short pulse on micro-ECM was analyzed, complementary chopper circuit was presented to avoid waveform distortion, which can achieve higher pulse frequency. A fast protect circuit was designed, and its response time is less than 5μs, which can avoid damaging workpiece and electrical components by switching off machining voltage and step motor as soon as a short circuit was detected. A series of ECM experiments using the power supply have been carried out, and results of test have proved that high frequency, short pulse width power supply helps to achieve better quality surface, higher machining accuracy.

Abstract: In the treatment of disorders, bio-electrodes are used to be implanted into the patients’ deep brain for long-term stimulation. This paper presents a custom design and flexible fabrication process of bio-electrode for treating neural disorders using rapid prototyping (RP) technique. A 3D model of the bio-electrode is designed and the photosensitive resin electrode prototype is fabricated on the laser rapid prototyping machine, and then the bio-electrode is fabricated using this electrode prototype and the silicon rubber mold and winding technique. The spatial distribution of the electric field fabricated of the bio-electrode is analyzed, and the optical photomicrograph reveals that the cylindrical surfaces of the polyurethane of the bio-electrode have smooth surface and no visible microcracks, and the spiral lines are arranged densely and have no defects of loose and falling and partly protruding. The electrochemical experiments show that the electrochemical process of the bio-electrode is reversible and the bio-electrode has good functionality and stability property.

Abstract: Mold Decomposed Injection Sculpturing (Mold DIS) is a rapid prototyping technique for producing complex shaped fugitive wax molds. Metallic materials have been used to make parts from these molds. This paper describes the Mold DIS method and an automated mold building machine based on the integration of a CNC sculpture machine and a wax injection device. Material selection, process parameters determination and equipment issues are explained. A 316L stainless steel turbine part with feature sizes ranging from 2 to 50 mm will be shown.

Abstract: The cutting performance (tool wear, surface roughness of machined work-piece and chip formation)of wet, dry and Minimum Quantity Lubrication (MQL) machining when milling of high strength steel (PCrNi2Mo) using cemented carbide tools under different (cutting speed, depth of cut, feed rate) was analyzed. The experimental results showed that as the cutting speed, depth of cut and feed rate changed, MQL conditions provided the lowest flank wear and the highest surface quality. Chip formation produced under MQL conditions become more favorable in terms of color and shape. The results obtained prove the potential of using MQL technique in the milling process of high strength steel (PCrNi2Mo) for high cutting speed, feed rate and depth of cut.

Abstract: Numerical study on fatigue life of ZK60 magnesium alloy plate before and after laser shot peening (LSP) was carried out in this paper. Based on the FEA model, residual stress field induced by LSP was analyzed, the fatigue life and position of weak area were predicted with ABAQUS software and MSC.Fatigue code, respectively, and the processing parameters were optimized. The results show that the fatigue life of ZK60 sheet metal by single LSP with one side and both sides increased by 72.9% and 78.5% compared with the untreated sample respectively. The size and depth of compressive residual stress increase with the increment of peening number, but when the peening number gets to a certain value, the residual stress reaches saturation and the fatigue life increase no longer significantly.

Abstract: Taking account of the situation of many old-fashioned imported machine tools, this paper proposes some favourable methods of rebuilding equipment. In theory and practice, with full digital electric system of modern automation technology, rebuilt equipments are easy to operate and reduce energy consumption, raise production efficiency. It realizes the aim of Environment-friendly and resource-economical. In this paper, it also gives three typical examples of rebuilding equipment, table planning machine made in Germany, D2300 lathe and 745A slotter made in Russia. Some pragmatic issues have been discussed, e.g. design optimization for speed regulation of main drive, position finding of cutter frame and synchro control between lathe tools feeding and lathe chuck turning. Finally, it gives the results of the operational curves of rebuilding equipment and relevant data.